1. Field of the Invention
The present invention relates to a spindle motor and a bearing assembly for use in office automation equipment such as a computer and peripheral equipment thereof as a driving device/component for the rotating mechanism thereof, specifically to the spindle motor and the bearing assembly that achieve to enhance the run-out accuracy/nonrepeatable runout (NRR0) of a motor, and the reliability of the noises, acoustic life, and rigidity, etc.
2. Description of the Prior Art
The spindle motor for driving a magnetic disk on a hard disk drive as a peripheral equipment of a computer is classified broadly into two types in terms of the structure: the fixed shaft type in which a fixed shaft is installed upright on a base, and a rotor hub is supported to freely rotate by the fixed shaft through a bearing interposed between the fixed shaft and the rotor hub; and the rotary shaft type in which a rotary shaft is vertically installed on a rotor hub, and the rotary shaft is supported to freely rotate on a base through a bearing interposed between the rotary shaft and the base.
Generally, the fixed shaft type is provided with, as shown in FIG. 9, a base (flange) 02, a fixed shaft 010 that is installed upright on the base 02, a rotor hub (hub member) 03 that rotates relatively to the base 02, and a bearing means 04 interposed between the fixed shaft 010 and the rotor hub 03. A recording medium such as a magnetic disk (not shown) is mounted on the rotor hub 03. A stator 015 is installed on the outer peripheral surface of an inner cylindrical wall 014 of the base 02, and a permanent magnet 016 is installed on the inner peripheral surface of an outer circumferential wall 013 of the rotor hub 03 so as to face the outer peripheral surface of the stator 015. The symbol 017 denotes a feeder part to the windings of the stator 015, which is connected to a flexible printed circuit board 037.
The bearing means 04 employs a compound ball bearing, and an inner ring 06 thereof is applied from the outside to the fixed shaft 010 to be fixedly engaged with the shaft, and an outer ring 05 thereof is applied from the inside to the inner peripheral surface of an inner circumferential wall 032 of the rotor hub 03 to be fixedly engaged with the wall. A part of the inner ring 06 can be formed integrally with the fixed shaft 010 according to circumstances, as shown in FIG. 9; and the outer ring 05 can be formed commonly integrally throughout the whole structure of the compound ball bearing in certain cases, as shown in the same figure.
The rotary shaft type is also provided with, as shown in FIG. 10, the base (flange) 02, the rotor hub (hub member) 03 that rotates relatively to the base, a rotary shaft 020 that is vertically installed on the rotor hub 03, and the bearing means 04 interposed between the rotary shaft 020 and the base 02. The recording medium such as a magnetic disk (not shown) is mounted on the rotor hub 03. The stator 015 is installed on the outer peripheral surface of the inner cylindrical wall 014 of the base 02, and the permanent magnet 016 is installed on the inner peripheral surface of the outer circumferential wall 013 of the rotor hub 03 so as to face the outer peripheral surface of the stator 015. The symbol 017 denotes the feeder part to the windings of the stator 015, which is connected to a flexible printed circuit board 037.
The bearing means 04 employs a compound ball bearing, and the inner ring 06 thereof is applied from the outside to the rotary shaft 020 to be fixedly engaged with the shaft, and the outer ring 05 thereof is applied from the inside to the inner peripheral surface of the cylindrical wall 014 of the base 02 to be fixedly engaged with the wall. A part of the inner ring 06 can be formed integrally with the rotary shaft 020 according to circumstances, as shown in FIG. 10; and the outer ring 05 can be formed commonly integrally throughout the whole structure of the compound ball bearing in certain cases, as shown in the same figure.
In a certain case, the rotor hub 03 and the rotary shaft 020 each manufactured separately can be assembled in a unit, as shown in FIG. 10; and in another case, they can be manufactured in an integral unit from the beginning. In the latter case, a part of the inner ring 06 cannot be formed integrally with the rotary shaft 020.
In any type of the spindle motor 01, the rotor hub 03 thereof is supported on the base 02 to freely rotate through the compound ball bearing 04 as a rolling bearing interposed between the base 02 and the rotor hub 03. And, the inner ring 06 of the compound ball bearing 04 is applied from the outside to the fixed shaft 010 vertically installed on the base 02 or to the rotary shaft 020 vertically installed on the rotor hub 03 to be fixedly engaged therewith. The outer ring 05 thereof is applied from the inside to the inner peripheral surface of the inner circumferential wall 032 of the rotor hub 03 or to the inner peripheral surface of the inner cylindrical wall 014 of the base 02 to be fixedly engaged therewith.
Now, the recent demand in the hard disk drive shows a remarkable tendency to increase the recording capacity, to enhance the impact resistance, to lower the noises, to increase the data access speed, and so forth. In order to answer these requirements, the rolling bearing of a spindle motor has gone through improvements of the material composition, enhancements of the working precision of the inner and outer rings and rolling elements, etc.
However, when the inner and outer rings and the balls (rolling elements) are made of the steels such as the bearing steels, there occur metal contacts between the rolling surfaces of the inner and outer rings and the surfaces of the balls, which effects galling and wearing to deteriorate the acoustic characteristic, leading to the problem of the acoustic life (recently, the life of the spindle motor is evaluated not by the fatigue life, but by the acoustic life). Further, there occur fretting corrosions (impressions, dilapidated surfaces) on the rolling surfaces due to shocks and vibrations during transportation, which also deteriorates the acoustic life and the precision of rotation.
Especially in recent years, the rotational speed of a spindle motor is increased to higher than 7200 rpm, and the rotating sound of the motor becomes increased to that degree, which tends to shorten the acoustic life. Also in future, a still more increase of the recording capacity is estimated in view of the demand of recording video images and so forth. In order to answer such demands and future problems estimated, the foregoing improvements of the material composition and enhancements of the working precision and the like will not be sufficient for the countermeasure.
In recent years, the ball materials have been tested and examined which exceed in the non-agglutination property and the wear resistance, and the nitride silicon ceramics has been adopted as the rolling element material. There have been discussions about the limitation of the rolling bearing itself, including the ceramic ball bearing made of such new materials, and it has been put forward to employ the fluid bearing in order to solve these problems.
FIG. 11 illustrates a rotary shaft type spindle motor 01 with such a fluid bearing loaded. This spindle motor 01 is provided with the base (flange) 02, the rotor hub (hub member) 03 that rotates relatively to the base 02, a rotary shaft 020 that is vertically installed on the rotor hub 03, and a fluid bearing 030 interposed between the rotary shaft 020 and the base 02.
A sleeve 031 of the fluid bearing 030 sheathes the rotary shaft 020, and is applied to the inner peripheral surface of the inner cylindrical wall 014 of the base 02 to be fixedly engaged with the wall. A lubricating oil is supplied into the sliding area between the sleeve 031 and the rotary shaft 020, and herringbones ( less than -shaped grooves) 033 formed on the circumferential surface of the rotary shaft 020 effect to raise the pressure of the lubricating oil, along with the rotation of the rotary shaft 020, which floats the rotary shaft 020 up from the sleeve 031.
Although not detailed in the drawing, similar herringbones are formed on an edge surface of a thrust ring 034 fixedly engaged with the lower part of the rotary shaft 020, and a lubricating oil is supplied into a gap between the edge surface and an inner surface of a counter plate 037 fixedly engaged with the lower end of the sleeve 031. And, as the rotary shaft 020 turns, the herringbones effect to raise the pressure of the lubricating oil, which makes the counter plate 037 receive the thrust that acts on the rotary shaft 020.
Therefore, the base 02 supports the rotary shaft 020 of the rotor hub 03 to freely rotate through the fluid bearing 030 interposed therebetween. The other structure of the motor is basically identical to the spindle motor having the compound ball bearing used therein.
On the other hand, in the fixed shaft type spindle motor with a fluid bearing loaded, which is not illustrated, the sleeve 031 of the fluid bearing 030 is fit to an inner peripheral surface of a wall formed on the rotor hub 03, and a fixed shaft is installed upright on the base 02. And, this fixed shaft is sheathed with the sleeve 031. Therefore, the fixed shaft supports the rotor hub 03 to freely rotate through the fluid bearing 030 interposed therebetween.
Even though either the ball bearing or the fluid bearing is used, and even though the spindle motor is the fixed shaft type or the rotary shaft type, the installation of the bearing in the spindle motor is carried out by any one of the methods: press fitting to the counterpart (rotating components and fixed components), adhesion by adhesives, and press-fit adhesion using both of these.
In case of the press fitting method, the shape precision (circularity, cylindricality, surface roughness) of the inner or outer peripheral surface of the counterpart gives influence to transfer the shape from the outer peripheral surface of the outer ring and the inner peripheral surface of the inner ring of the rolling bearing to the rolling surfaces of the inner and outer rings, or to deform the rolling surfaces of the inner and outer rings. Also, the external stress caused by a press fitting propagates through the outer peripheral surface of the outer ring or through the inner peripheral surface of the inner ring, and produces permanent deformations on the rolling surfaces of the inner and outer rings through the rolling elements to give impressions thereon, which deteriorates the reliability of the run-out accuracy/NRR0, the noises, and the acoustic life, etc., of the motor. In the fluid bearing, the clearance between the sleeve and the shaft sheathed with the sleeve varies, which varies the rigidity.
And, in case of the adhesion, the stress is produced when the adhesive is hardened, which deforms the bearing, also deteriorating the reliability of the run-out accuracy, the noises, and the acoustic life of the motor, and so forth. Further, in the rotary shaft type spindle motor, the assembly of the stator 015 on the outer peripheral surface of the cylindrical wall 014 of the base 02 gives influence to deteriorate the accuracy of the inner diameter of the cylindrical wall 014, which brings about deterioration of the bearing accuracy.
Further, in case of the foregoing press fitting, adhesion, or press-fit adhesion being adopted as the method of mounting the bearing, an adhesion groove (refer to adhesion groove 040 in FIG. 9, adhesion groove 041 in FIG. 10) for filling adhesives and a run-off groove are needed on the bearing mounting surface on the side of the counterpart, which increases the man-hour to that extent, leading to cost increase.
The present invention has been made in view of the foregoing circumstances, and it is an object of the invention to provide a spindle motor and a bearing assembly that achieve to resolve the foregoing problems of the conventional spindle motor, to remove bad influences on the precision of the rolling surfaces of the inner and outer rings through the outer peripheral surface of the outer ring and the inner peripheral surface of the inner ring of the bearing, by the stress resulting from the shape precision (circularity, cylindricality, surface roughness) of the inner or outer peripheral surface of the counterpart in mounting the bearing, or the stress caused by the press fitting, adhesion, or press-fit adhesion as the method of mounting the bearing, to enhance the reliability of the run-out accuracy/NRR0, the noises, and the acoustic life, etc., of the spindle motor, and to reduce the manufacturing cost thereof.
According to the first aspect of the invention, the spindle motor to resolve the above problems is a fixed shaft type spindle motor in which a fixed shaft is vertically installed on a base and a rotor hub is supported to freely rotate by the fixed shaft through a bearing, wherein the bearing is a compound ball bearing, a larger diameter portion of a stepped top-form connection member having the larger diameter portion and a smaller diameter portion is fixedly engaged with an upper end of an outer ring of the compound ball bearing, and the smaller diameter portion of the connection member is fastened to the rotor hub.
Therefore, when the bearing is composed of the compound ball bearing, the outer ring of the compound ball bearing is to be fastened to the rotor hub through the connection member.
As a result, the rotor hub (the component on the rotating side) being one of the two counterparts (the component on the rotating side and the component on the fixing side) that mount the compound ball bearing can be made up without the inner peripheral surface of a wall, which has conventionally been regarded as necessary to fit the outer ring of the compound ball bearing thereto. Therefore, there does not exist the stress resulting from the shape precision (circularity, cylindricality, surface roughness) of the inner peripheral surface of the wall, or the stress caused by the press fitting, adhesion, or press-fit adhesion as the method of mounting the bearing; accordingly disappear bad influences on the precision of the rolling surfaces of the inner and outer rings through the outer peripheral surface of the outer ring of the bearing, thereby enhancing the reliability of the run-out accuracy/NRR0, the noises, and the acoustic life, etc., of the spindle motor.
Further, since the rotor hub being the one of the two counterparts that mount the compound ball bearing can be configured without the inner peripheral surface of the wall, which has conventionally been regarded as necessary to fit the outer ring of the compound ball bearing thereto, the adhesion groove (the groove for filling adhesives) and the run-off groove that are formed conventionally on the inner peripheral surface of the wall become unnecessary, thereby reducing the man-hour to lower the manufacturing cost.
According to the second aspect of the invention, there is provided a fixed shaft type spindle motor in which a fixed shaft is vertically installed on a base and a rotor hub is supported to freely rotate by the fixed shaft through a bearing, wherein the bearing is a fluid bearing, a larger diameter portion of a stepped top-form connection member having the larger diameter portion and a smaller diameter portion is fixedly engaged with an upper end of a sleeve of the fluid bearing, and the smaller diameter portion of the connection member is fastened to the rotor hub.
Therefore, when the bearing is composed of the fluid bearing, the sleeve of the fluid bearing is to be fastened to the rotor hub through the connection member.
As a result, the rotor hub (the component on the rotating side) being one of the two counterparts (the component on the rotating side and the component on the fixing side) that mount the fluid bearing can be made up without the inner peripheral surface of a wall, which has conventionally been regarded as necessary to fit the sleeve of the fluid bearing thereto. Therefore, there does not exist the stress resulting from the shape precision (circularity, cylindricality, surface roughness) of the inner peripheral surface of the wall, or the stress caused by the press fitting, adhesion, or press-fit adhesion as the method of mounting the bearing; accordingly disappear bad influences on the precision of the sliding surfaces of the sleeve and the fixed shaft and the clearance between the sliding surfaces of the two through the outer peripheral surface of the sleeve of the bearing, thereby enhancing the reliability of the run-out accuracy/NRR0, the noises, the acoustic life, and the rigidity, etc., of the spindle motor.
Further, since the rotor hub being the one of the two counterparts that mount the fluid bearing can be configured without the inner peripheral surface of the wall, which has conventionally been regarded as necessary to fit the sleeve of the fluid bearing thereto, the adhesion groove and the run-off groove that are formed conventionally on the inner peripheral surface of the wall become unnecessary, thereby reducing the man-hour to lower the manufacturing cost.
According to the third aspect of the invention, there is provided a rotary shaft type spindle motor in which a rotary shaft is vertically installed on a rotor hub and the rotary shaft is supported to freely rotate on a base through a bearing, wherein the bearing is a compound ball bearing, a larger diameter portion of a stepped top-form connection member having the larger diameter portion and a smaller diameter portion is fixedly engaged with a lower end of an outer ring of the compound ball bearing, and the smaller diameter portion of the connection member is fastened to the base.
Therefore, when the bearing is composed of the compound ball bearing, the outer ring of the compound ball bearing is to be fastened to the base through the connection member.
As a result, the base (the component on the fixing side) being the other one of the two counterparts (the component on the rotating side and the component on the fixing side) that mount the compound ball bearing can be made up without the inner peripheral surface of a wall, which has conventionally been regarded as necessary to fit the outer ring of the compound ball bearing thereto. Therefore, there does not exist the stress resulting from the shape precision (circularity, cylindricality, surface roughness) of the inner peripheral surface of the wall, or the stress caused by the press fitting, adhesion, or press-fit adhesion as the method of mounting the bearing; accordingly disappear bad influences on the precision of the rolling surfaces of the inner and outer rings through the outer peripheral surface of the outer ring of the bearing, thereby enhancing the reliability of the run-out accuracy/NRR0, the noises, and the acoustic life, etc., of the spindle motor.
Further, since the base being the other one of the two counterparts that mount the compound ball bearing can be configured without the inner peripheral surface of the wall, which has conventionally been regarded as necessary to fit the outer ring of the compound ball bearing thereto, the adhesion groove and the run-off groove that are formed conventionally on the inner peripheral surface of the wall become unnecessary, thereby reducing the man-hour to lower the manufacturing cost.
According to the fourth aspect of the invention, there is provided a rotary shaft type spindle motor in which a rotary shaft is vertically installed on a rotor hub, and the rotary shaft is supported to freely rotate on a base through a bearing, wherein the bearing is a fluid bearing, a larger diameter portion of a stepped top-form connection member having the larger diameter portion and a smaller diameter portion is fixedly engaged with a lower end of a sleeve of the fluid bearing, and the smaller diameter portion of the connection member is fastened to the base.
Therefore, when the bearing is composed of the fluid bearing, the sleeve of the fluid bearing is to be fastened to the base through the connection member.
As a result, the base (the component on the fixing side) being the other one of the two counterparts (the component on the rotating side and the component on the fixing side) that mount the fluid bearing can be made up without the inner peripheral surface of a wall, which has conventionally been regarded as necessary to fit the sleeve of the fluid bearing thereto. Therefore, there does not exist the stress resulting from the shape precision (circularity, cylindricality, surface roughness) of the inner peripheral surface of the wall, or the stress caused by the press fitting, adhesion, or press-fit adhesion as the method of mounting the bearing; accordingly disappear bad influences on the precision of the sliding surfaces of the sleeve and the fixed shaft and the clearance between the sliding surfaces of the two through the outer peripheral surface of the sleeve of the bearing, thereby enhancing the reliability of the run-out accuracy/NRR0, the noises, the acoustic life, and the rigidity, etc., of the spindle motor.
Further, since the base being the other one of the two counterparts that mount the fluid bearing can be configured without the inner peripheral surface of the wall, which has conventionally been regarded as necessary to fit the sleeve of the fluid bearing thereto, the adhesion groove and the run-off groove that are formed conventionally on the inner peripheral surface of the wall become unnecessary, thereby reducing the man-hour to lower the manufacturing cost.
Further, according to the fifth aspect of the invention, the bearing assembly to resolve the foregoing problems is a bearing assembly in which an inner ring of a compound ball bearing with a pressurization applied is fixedly engaged with a shaft, and a larger diameter portion of a stepped top-form connection member having the larger diameter portion and a smaller diameter portion is fixedly engaged with any of ends of an outer ring of the compound ball bearing.
Therefore, since the bearing assembly according to the fifth aspect of the invention is made up as above, the compound ball bearing, the shaft, and the connection member are assembled in advance into one assembly unit. As a result, fastening the shaft to the one of the two counterparts (the component on the rotating side and the component on the fixing side) that mount the bearing assembly and fastening the smaller diameter portion of the connection member to the other one will achieve to assemble the compound ball bearing between the two counterparts, and thus the mounting work of the compound ball bearing becomes extremely easy to perform.
And, according to the sixth aspect of the invention, there is provided a bearing assembly in which a sleeve of a fluid bearing sheathes a shaft, and a larger diameter portion of a stepped top-form connection member having the larger diameter portion and a smaller diameter portion is fixedly engaged with any of ends of the sleeve.
Therefore, since the bearing assembly according to the sixth aspect of the invention is made up as above, the sleeve of the fluid bearing, the shaft, and the connection member are assembled in advance into one assembly unit. As a result, fastening the shaft to the one of the two counterparts (the component on the rotating side and the component on the fixing side) that mount the bearing assembly and fastening the smaller diameter portion of the connection member to the other one will achieve to assemble the fluid bearing between the two counterparts, and thus the mounting work of the fluid bearing becomes extremely easy to perform.